1. Field of the invention
The invention relates to a relay apparatus between relative rotary members which connect rotary members electrically through a cable.
2. Description of the Related Art
According to conventional relay apparatus between relative rotary members, for example, if an inner cylindrical portion rotates counterclockwise, the cable moves to wind around the inner cylinder. Therefore, the cable outside of the C-shaped mobile body is contacted with the outer circumferential side of the mobile body. Furthermore, while the cable is contacted to one end of the mobile body, the cable is reversed and passes inside the mobile body, and the cable winds around the inner cylinder. In this case, the one end of the mobile body is pushed by the cable, so that the mobile body rotates counterclockwise.
When the inner cylinder rotates clockwise toward the outer cylinder, the cable which is wound around the inner cylinder unwinds outward from the inner cylinder. Thus, the cable which is wound around the inner cylindrical portion contacts the inner circumferential side of the mobile body. Furthermore, when the cable is contacted with the other end portion of the mobile body, the cable is reversed and passes outside of the mobile body. Thereby, the cable is contacted with an inside of the outer cylindrical portion. In this case, the other end portion of the mobile body is pushed by the cable, so that the mobile body rotates clockwise.
In relay apparatus between relative rotary members, when the inner cylinder rotates clockwise, the cable is rewound. While the cable is contacted with the inner circumferential surface, the cable moves. The moving direction of the cable is the direction of the tangent of the inner circumferential surface. Since the inner circumferential surface is curved, it presses against the front of the cable. Therefore, the cable has a high moving resistance. Accordingly, the cable generates a compressive stress. More particularly, the cable located between the one end element of the mobile body and the other aperture may buckle, so that the cable rises outward. Since such buckling shortens a life of a cable, it is essential to prevent buckling. Accordingly, there may also be provided an apparatus having a protrusion which is installed at the inner circumferential side in order to reduce sleeve resistance. However, when such protrusion is installed, a moving resistance is caused rather than reduced due to this protrusion.